Rönnberg, Sarah

Abstract [en]

This thesis work has focused on conducted emission (up to 150 kHz) from common lowvoltage appliances. The emphasis has been on equipment that contributes to a sustainable energy system: photovoltaic (PV) installations and energy-saving lamps (LED lamps). The frequency components present in the grid in addition to the fundamental 50 Hz component can be divided into harmonics (up to 2 kHz in a 50 Hz system) and supraharmonics (2 kHz to 150 kHz). These frequency components are partly the effect of normal operation of equipment due to power-electronic converters and the switching technique used. Power line communication, PLC, is an important source of frequency components in the range 9 to 95 kHz. Even though from an equipment viewpoint there is no difference between a signal used for communication and a signal that is a residue from a switching circuit, PLC is a useful signal for operation of the grid and for communication with electricity meters. The amplitude of the communication signal is in in almost all cases higher than the emission from any other equipment connected to the grid.Understanding the different types of interaction between PLC and end-user equipment has been a major part of this work. Five types of interaction have been identified; some negative for PLC, some negative for end-user equipment. An important conclusion from this part of the work is that loss of communication with PLC, as is often reported with remote reading of electricity meters, is not due to emission by end-user equipment but due to the EMC filter of the end-user equipment providing a low-impedance path. The understandings acquired from the work with PLC have been applied to other types of emission as well. Supraharmonics from individual devices, above about 10 kHz, flow mainly to neighboring devices, not into the grid. This behavior was found by laboratory experiments and confirmed by other studies as well. A circuit-theory model has been developed that explains this behavior. The EMC filters are shown to be the main cause of this behavior. Other configurations of those filters may result in a larger flow of emission towards the grid.One type of appliance that has been introduced recently is the LED lamp. LED lamps come in different designs with different emission spectra. A possible distinction is between lamps with high levels of low-order harmonics (up to a few 100 Hz) and those with high levels of supraharmonics. Restricting the emission in the lower frequency range, through standardization, could result in higher distortion levels at higher frequencies. Replacement of incandescent lamps by CLF and LED lamps is not expected to result in a noticeable increase in harmonic voltage and current levels in the grid. This has been shown through several laboratory experiments and field experiments.Emission from PV inverters is low at low-order harmonics, this have been shown by a number of measurements both on single phase connected installations, so called rooftop installations and larger, three phase connected installations (20 kW). In addition to emission in the low frequency range, PV inverters emit at their switching frequency, e.g. around 16 kHz. The emission at this frequency is shown to vary by a factor of 5 or more, depending on the presence of neighboring equipment. This was shown by measurements and has been explained by a circuit-theory model. This thesis work has resulted in further understanding on the emission from PV panels and energy-saving lamps and on the propagation of conducted emission from common household appliances. This work is an important contribution to the research on distortion of voltage and current in the frequency range 2 to 150 kHz.